1. Field of the Application
The present application relates to dual-flow axial turbomachines. More specifically, the present application relates to the splitter nose of a dual-flow axial turbomachine, the nose splitting the incoming airflow into a primary and a secondary flow. More precisely, the present application relates to de-icing the splitter nose.
2. Description of Related Art
In order to optimise their thrust jet engines have several annular airflows. A primary flow passes through a compressor and a combustion chamber and is then expanded in a turbine. A secondary flow bypasses the compressor, the combustion chamber and the turbine, and then rejoins the main flow at the outlet of the jet engine. The flows are separated by a splitter nose located upstream of the compressor. Its shape enables it to divide the airflow entering the turbomachine and restricts entry to the compressor. Being located downstream of the blades of the inlet fan, it is exposed to the ingestion of foreign objects.
The air entering the turbomachine is at the atmospheric temperature at the splitter nose. These temperatures can drop to −50° C. at altitude. In the presence of moisture, ice can form on the nose. During flight, this ice can expand and build up into blocks at the tips of the compressor stator blades.
These blocks can change the geometry of the nose and affect the flow of air entering the compressor, which can reduce performance. As they increase in size the blocks can become particularly heavy. Thereafter, they may break off and be ingested by the compressor, which could damage the rotor and stator blades. This ingestion is particularly damaging as it has not first passed through the inlet fan.
To limit such ice formation, splitter noses are fitted with de-icers.
U.S. Pat. No. 6,561,760 B2 discloses a system for de-icing the splitter nose using exhaust gases. The nose is formed of an outer wall and an outer shell. The latter supports an annular row of stator blades. The splitter nose comprises a circular slit which houses an upstream edge of the outer shell. The slit interface is made so as to form axial channels through the thickness of the elements. These channels allow exhaust gas to circulate, which has the effect of heating the leading edge of the splitter nose. The latter is thus well protected against ice formation. However, this solution requires complex machining operations. Efficiency is mainly concentrated in the channels and depends on the thermal conductivity of the materials. It would be difficult to choose another material, say a stronger or lighter one, if the thermal conductivity is low. Also, this system requires that a portion of the exhaust gases from the jet engine are discarded.
Another known solution is to use oil that needs to be cooled to do the de-icing. This oil can be engine oil or actuator oil the control of whose temperature maintains the turbojet and keeps it operating in optimum conditions.
Patent EP 2075194 A1 discloses an oil-air heat exchanger for cooling the oil in a jet engine. The heat exchanger comprises an oil circuit arranged inside the splitter nose. The circuit may be located on an inner face of the splitter nose or in its thickness. This system allows the nose to be de-iced effectively while cooling the oil. This exchanger is, however, complicated to implement. Its effectiveness can be reduced at the upstream end of the splitter nose when this is thick, for example for reasons of mechanical strength.
Patent EP 1942249 A2 discloses a system for transferring heat to a turbomachine. The system comprises a set of pipes extending around the perimeter of the splitter nose of the turbomachine. On its perimeter, the pipes are housed in an annular cavity between the walls delimiting the primary and secondary flows. The pipes are mechanically protected. As they are pressed against the wall defining the secondary flow, they enable heat conduction that promotes defrosting. However, the effectiveness of the pipe is reduced at the leading edge of the splitter nose due to the distance which separates them. The tip of the nose is massive, and therefore has a high thermal inertia. When the system must operate in a discontinuous manner, it is less responsive. Due to variations in thickness of the elements in the vicinity of the pipe, one part may be cold while another is hot, or at least at a temperature well above what is required for defrosting. The operation of such a system is not homogeneous. Also, the tube is located primarily in the upper or outer part (with respect to the axis of rotation of the machine) of the nose. It is less effective in the lower part (or internal), and may allow ice to develop on the outer shell of the stator.
Although great strides have been made in the area of dual-flow axial turbomachines, many shortcomings remain.